The disclosed embodiments of the present invention relate to processing an image data, and more particularly, to an image data compression apparatus employed in an overdrive application and capable of compressing an image data of a second frame according to a first frame preceding the second frame and related image processing method thereof.
Data compression is commonly used to reduce the amount of data stored in a storage device. Regarding an overdrive technique applied to a liquid crystal display (LCD) panel for example, it artificially boosts the response time by increasing the driving voltage used to make a liquid crystal cell change its state. The overdrive voltage of one liquid crystal cell (i.e., one pixel) is determined by a pixel value in a current frame and a pixel value in a previous frame. Therefore, an image data of the previous frame has to be recorded into a frame buffer for later use. In general, the image data of the previous frame will be compressed before stored into the frame buffer, and the compressed data of the previous frame will be read from the frame buffer and decompressed to produce a recovered image data of the previous frame.
If a compression approach which provides a lower compression ratio is employed to compress the image data of the previous frame, the frame buffer is required to have a greater storage capacity and higher bandwidth. However, if a compression approach which provides a higher compression ratio is employed to compress the image data of the previous frame, a difference (error) between an original image data and a recovered image data derived from the compressed image data will become more significant, leading to degradation of the final display quality. In addition, the storage capacity of the frame buffer is generally determined according to a desired compression ratio. Thus, the bandwidth of the frame buffer has an upper bound due to the desired compression ratio. However, there is no lower bound for the bandwidth. Therefore, it is possible that a compression approach which provides a higher compression ratio is employed to compress a frame with simple image contents. As a result, only part of the bandwidth is used and the image output quality of the frame with simple image contents is degraded because of the higher compression ratio. Therefore, the conventional design may not properly use the available bandwidth for achieving optimized image output quality.
In view of above, there is a need for an image data processing apparatus and method which can meet a compression ratio criterion of the frame buffer without sacrificing the image output quality.